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A taxonomic key, based on restriction enzyme analysis of the second internal-transcribed spacer (ITS-2) in the nuclear ribosomal DNA gene, was developed for identification of 17 Ixodes tick species in the United States. This key includes: Ixodes affinis Neumann, Ixodes angustus Neumann, Ixodes baergi Cooley and Kohls, Ixodes brunneus Koch, Ixodes cookei Packard, Ixodes dentatus Marx, Ixodes jellisoni Cooley and Kohls, Ixodes kingi Bishopp, Ixodes minor Neumann, Ixodes muris Bishopp and Smith, Ixodes pacificus Cooley and Kohls, Ixodes scapularis Say, Ixodes sculpularis Neumann, I. spinipalpis Hadwen and Nuttall, Ixodes texanus Banks, Ixodes uriae White, and Ixodes woodi Bishopp. A 900-bp fragment of the ITS-2 was amplified using the polymerase chain reaction. This fragment was then digested with the restriction enzymes MspI and CfoI, and the digested fragments were size fractionated on a 2.5% high-resolution agarose gel. A dichotomous key was developed based on digested fragment sizes relative to a standard set of size markers. Little intraspecific variation in restriction fragment banding patterns was detected.

A morphological study of the larval stage of the blacklegged tick, Ixodes scapularis, was conducted to further examine congruence between northern and southern morphotypes. Preliminary ANOVA revealed that 9 characters were not significantly different; thus 28 characters were used in analyses of a total of 8 groups of I. scapularis originally from Minnesota, Massachusetts, Maryland, Missouri, North Carolina, Georgia, F1 progeny of reciprocal crosses of ticks from Massachusetts and Georgia, and I. pacificus from California. Principal components (PC) analysis identified seven setal (sternal, preanal, 3 scutal, central, and marginal dorsal) and 3 nonsetal characters (interauricular distance, hypostome internal file, and coxa I internal spur) with positive static allometries. All Mahalanobis distances in canonical variate analyses (CVA) including and excluding I. pacificus and setal characters were significantly different. Scatterplots from PC and CVAs separated I. pacificus from all other groups in the first axis; the second function arranged groups in a pattern related to latitude. Unlike the results of previously reported nymphal analyses, no multivariate effect related to longitude was revealed; however, Missouri larvae had the shortest values for 2 setal and 9 nonsetal characters. As in nymphs, frequency polygons revealed an overlapping/continuous pattern, indicative of clinal geographic variation.

This is the first report of natural infection by Borrelia burgdorferi in the cotton rat Sigmodon hispidus. Nine B. burgdorferi isolates were obtained from ear tissues, urinary bladders, or both, by culturing tissues in BSKII medium. The rat from which the SI-3 isolate was cultured was from the same site (Sapelo Island, Georgia) as an infected cotton mouse Peromyscus gossypinus and Ixodes scapularis tick reported previously. The 8 B. burgdorferi isolates from rats in Florida included 1 (AI-1) from Amelia Island, 1 (FD-1) from Faver-Dykes State Park, and 6 (MI-3 through MI-8) from Merritt Island. The distance between Sapelo Island and Merritt Island is approximately 400 km. All B. burgdorferi isolates were characterized by indirect immunofluorescence using monoclonal antibodies to OspA (H3TS, H5332) and OspB (H5TS, H6831), polymerase chain reaction detection of specific B. burgdorferi B-31 DNA target sequences (ospA, fla, and a random chromosomal sequence), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of spirochetal proteins. The phenotypic and genotypic characteristics of the isolates are discussed, as well as the probable importance of the cotton rat as a reservoir for B. burgdorferi in the southern United States.

New host and distributional records, seasonal activities in Georgia, laboratory rearing data, and taxonomic description of nymphal and larval Ixodes affinis are presented. Our data expand the list of known natural hosts of this species, record for the first time several natural hosts of larvae and nymphs, provide information on feeding periods of all stages, preecdysial intervals, preovipositional, ovipositional, and incubational periods, as well as provide information on fecundity. The immatures are fully described and SEM micrographs of them are presented.